fn main() {
    let mut list = vec![1, 2, 3];

    {
        let list_first = list.first();
        let list_last = list.last();

        println!(
            "The first element is {:?} and the last is {:?}",
            list_first,
            list_last,
        );
    }

    *list.first_mut().expect("list was empty") += 1;
}
